Expansion screws for insertion in holes in concrete or rock walls for retaining machine parts are well known, and are available in many different forms. Most often, an expansion screw has one, or only a few means for expanding an associated sleeve, but expansion screws with a plurality of expander cones are known, for example, from German Published Patent Application Nos. 2138246 and 1814485.
Such expansion screws with a plurality of expander cones are intended to distribute the pressure of the sleeve over a large portion of the hole wall so that the surface pressure will be kept to a low value. Among the known expansion screws, are those having a sleeve with a crennelated profile. However, such a sleeve has its profile flattened when the screw is loaded and the walls of the hole consist of a very hard material, whereby the screw can then be pulled out of the hole.